This research program project includes the following studies: 1. Normal Development of Nervous System in Humans, to be carried out on the embryos and fetuses of the Carnegie Collection and on others to be collected, and including detailed studies of: (a) The normal sequence of development of the central and peripheral nervous system, skull, vertebrae, and limbs in staged embryos, so as to provide an accurate morphological base for analysis of congenital defects and malformations. (b) The growth and maturation of the fetal nervous system, skull, vertebrae, and limbs, especially with respect to the downgrowth of tracts such as the pyramidal through highly organized and functioning brain stem and spinal cord. Again, particular attention will be paid to correlation with congenital defects and malformations.